Darkness alarm



Dec. 6, 1949 A. H. LAMB 2,490,639

DARKNESS ALARM Filed NOV. 8, 1948 (vif d Patented Dec. 6, 1949 UNITEDSTATES PATENT OFFICE DARKNESS ALARM Anthony H. Lamb, Hillside, N. J.,assighor to Weston Electrical Instrument Corporation, Newark, N. J., acorporation of New Jersey Application November 8, 1948, Serial No.58,981

(Cl. Z50- 206) 8 Claims.

This invention relates to darkness alarms which develop a signicantsignal at the approach of inadequate illumination in a school room, anofce or shop where close visual tasks are performed, and moreparticularly to readily -portable darkness alarms of small size whichmay be placed on and moved about on a desk or work bench.

The human eye endeavors to compensate for variations in light intensityand does not warn against inadequate lighting until eyestrain, headacheor other results of decreased lighting develop to advise the .workerthat the lighting has been inadequate for some time. Photoelectricequipment for the measurement of light intensity is well known, but Suchlight meters have not included a visual or audible 'signal forindicating a decrease of the lighting below the value appropriate forthe particular work, such as reading, sewing or shop work, which is tobe performed. The light meters have been very useful in thedetermination of the articial illumination which is adequate for varioustypes of work but have been of little or no utility so far as concernsan indication of the appropriate time for turning on lights tocompensate for decreasing daylight illumination of the room or shop.

Objects of the invention are to provide darkness alarms, andparticularly small or miniature darkness alarms, which develop asignificant signal when the lighting falls below the value which shouldbe maintained for the work which is to be performed. An object is toprovide a, small, self-contained and readily portable darkness alarmwhich may be placed on and moved about 1 a desk or shop bench. Anotherobject is to provide a small and readily portable darkness alarm v whichis energized from the customary light or power circuit.

These and other objects and the advantages of the invention will beapparent from the following specification when taken with theaccompanying drawings in which:

Fig. 1 is a rear elevation of a darkness alarm embodying the invention,but with the rear cover and dry cells removed;

Figs. 2 and 3 are respectively a front elevation of and central verticalsection through the same; and

Fig. 4 is a front elevation of a darkness alarm on the b-ase by anyappropriate means. The contact arm 6 carries a small magnetic materialcontact 'I for cooperation with a stationary magnetized contact 8. Apendulum type of mechanism for separating the magnetic contacts, afteran engagement thereof, takes the form of a lever 9 pivotally supportedfor movement about an axis parallel to the sides of the instrumentcasing by a bracket I0 secured to the base I, the lower end of the leverbeing weighted and the upper end being provided with a soft rubbersleeve II.

The overall lsize and the detailed construction of the sensitive relaymay be Varied as desired but it is usually preferable to employ a relayof small size such as, for example, the illustrated miniature relaywhich, as now manufactured and sold as Model 813 by Weston ElectricalInstrument Corporation, has a base of 1.5 by 2.1 inches.

A photocell I2 of the barrier layer type is supported on and above theyoke portion of magnet 5 by spacing bushings I3 and screws I4. The backelectrode of the photocell is grounded on the magnet 2, and is therebyconnected in con- Ventional manner to the upper terminal of the movingcoil 5, i. e. through the upper jewel bridge and the upper spiralspring. The front electrode of the photocell I2 is connected to theother coil terminal by a line lead I2 which is soldered or Welded to acollector electrode spot on the front electrode and to the lower springsupport I5.

The base I is provided at, or approximately at, its center with anopening to receive a lamp socket I I having a center contact terminatingin a threaded screw I8 which extends through an opening in a metal strapI 9 and is secured thereto by a nut 20. Spring clips 2|, 22 for holdinga pair of miniature dry cells 23, 23 are mounted near the top and bottom"portions, respectively, of the base I by screws 24 which also serve tosecure T-shaped spring terminal strips 25, 26 to the clips 2i 22,respectively. The dry cells 23 are slipped into the spring clips 2I, 22in parallel arrangement, i. e. like cell terminals engage terminal strip25, and the other set of like cell terminals seat upon the terminalstrip 26. A lead 21 extends from the terminal strip 25 to the magnetizedcontact 8 of the relay, and a lead 28 is connected between the terminalstrip 25 and the shell of the lamp socket I'I. The center contact of thesocket is grounded on the metal strip I9, and this is in turn groundedon the magnet, and thereby on the relay contact arm 6, by a lead 29which extends from strip I9 to a soldering lug under one of the bolts 30which secures the magnet 4 to the base I. A rectangular cup-shaped metalshell 3| is slipped over and frictionally retained on the rim of thebase I to enclose the dry cells and associated elements.

A miniature lamp bulb 32 in the socket I'I is preferably of the type inwhich the outer end of the glass envelope is formed as a lens forfocussing the 'lghtbeamand the light bulb is ,entirely or substantiallyentirelywithinthe interior space of the C-shaped magnet 4`. Atransparent strip or sheet 33 of a colored plastic or glass, preferablyof red color, is cemented to the magnet to .overlie the lamp bulb. Themetal strap I9 which carries the lamp socket is not fixed ftoitheinstrument base I but may be moved back, after the dry cells areremoved, to the extent permitted by the soldered connecting wires, forremoval and replacement of the lamp bulb.

The moving coil 5 turns clockwise with'decreasing current therethrough,and the relay sensitivityfis so related ato vthephotocell output thatthe relay @contacts fl, felose Aat .la preselected Vcurrentcorresponding to the lower limit of illumination for'the to beperformed. The lamp circuit is thereby` completed toproduce a bright redglow within the `casing.v "Ifhe darkness alarm is placed atthe .-back:of :a desk or workbench in any convenient position such that it willnot interfere with -the'work to be performedbut will be Aquicklynoticedwhenthe lamp is lighted as a result of -decreasing solarillumination. The worker then turns'on lights in the room and resets thedarkness ,alarm :by :tilting thecasing about its right side, as viewedin Fig. 2, thereby turning the casing -with .respect to :the-,pendulumlever 9 to separate-the :magnetic contact l of arm lt from themagnetized icon-tact i8. l

When-.thus reset,.the darkness alarm may be returned to the desk or workbench to serve anew as an alarm in `.the :event that there areadditional lights which may vbe turned on when the solar illuminationdecreases to a lower value at which the further artificial illuminationis requi-red. Alternatively, the darkness alarm may be Aplaced with `itsIright side, as viewed in Fig. 2, on the desk :or wor-k bench, therebyrendering the alarm inoperative vsince the weighted reset lever S'wilthen hold `the relay contact 'arm away from the Vmagnet contact 8. Theala-rm may be rendered inoperative, for transport or shipping withoutdrain on the dry cells, by removing the rear closure 8.! and inserting apiece of paper or cardboard between the spring terminal I5 and theadjacent cell terminals.

An embodiment of the invention for operation inthe usual 1].0 voltalternating-current light and power circuit may be of somewhat simplerconstruction sincetherelay contacts l, 8 and resetting lever 9 can be,and preferably are, omitted, see Fig. 4. The lamp bulb is continuouslyenergized by means of a conventional two-wire conductor 34 and yplug 35,and the pointer 5' of the moving system carries an opaque vane or nag 35whichoverl-ies the focussing tip of the lamp bulb 32,50 long as thelightintensity at the photocell I2 is at or above the preselected minimumvalue for the work to be performed. As shown in Fig, 3, the lamp bulb isshielded laterally by the C-shaped magnet 4, and the observable red glowfrom the continuously energized lamp bulb 32 is negligible so long asthe opaque vane remains over the center of .thelenstip of .thebulb 32.YA stop 37 is supported by the rmagnet 4 to prevent the opaque flag 3 6from :moving beyond center position above the lamp bulb when thesolarillumination rises above the minimum value at which .the alarm isto operate.

The small size of the alarm will be apparent from Fig. 4 as the alarmdevice and the conventional electrical plug 35 are drawn to the samescale.

It is to be understood thatthe invention is not limited to theparticular embodiments herein illustrated and described since variousmodifications which may occur to those familiar with the design `andconstruction of relay circuits fall within the spirit and scope of myinvention as set forth inthe following lclaims.

I claim:

l. In a portable darkness alarm, a casing includinga base and .-a coverhaving a transparent top wall, an instrument carried by the base andincluding an approximately C-shaped permanent magnet and a pivotallymounted coil, a photocell and means supporting :the same 'beneath saidtransparent top wall of the casing-cover, means connecting sa-id`photocell acrosssaid ooi-l, a lamp bulb located within the interiorspace of and shielded laterally bythe magnet, and meanscontrolled bysaid coil upon `decrease Vin the illumination at the photocell -to apreselected value to radiate a light beam from said bulb through saidtransparent -wall of the-casing cover.

2. In a portable darkness alarm', the @invention as recited in claim l,wherein said means controlled -by said coil includesV a dry cellA,carried by said base, and circuite'lements including relay contactsoperable by s aid -coilgfor `completing an energizing circuit connectingvsaid lamp bulbwto said dry cell.

3. VIn aportable darkness alarm, the invention as recited in claim 2whereinsaid relaytcontacts are magnetic, incombinat'ion with manuallycon*- trolled means for resetting said magnetic con'- tacts after anengagement thereof.

Ll. In a portable darkness alarm, the invention as recited inclaim 3,wherein said resetting means includes a weighted lever operative uponturning said casing vto position the base thereof in a ver.- tical planeto separate said contacts, whereby said darkness alarm may be rendered.inoperative by turning said casing to rest upon a side wall thereof.

5. In a portable darkness alarm, the inventionl as recited in claim 3,wherein said resetting means includes a weighted lever pivoted forangular movement about an axis parallel to the sides of said casing, oneend of said lever being relatively movable upon tilting of the casingabout said axis to separate said contacts.

6. In a por-table darkness alarm, the invention as recited in claim 1,wherein a transparent colored Sheet overlies said lamp bulb.

7. In a portable darkness alarm, the invention as recited in claim l, incombination with a twowire conductor and plug for connecting said lampbulb to a source of current for continuous energization thereof, andwherein said means controlled by said coil includes a pointer and anopaque vane carried thereby for angular movement out of the path Aof thelight beam from said lamp bulb when the illumination falls `below thepreselected Value.

8. In a portable darkness alarm, the invention as recited in claim "7,in combination with a transparent colored sheet over said lamp bulb, andwherein said lamp bulb includes a lens for focussing the iight beamsubstantially upon said colored sheet.

ANTHONY H. LAMB.

yNo references cited.

